Formula
Each side is pixels divided by inches. The page keeps the smaller one:
DPI = minimum(pixel width / inches, pixel height / inches)
The print-size page divides pixels by a DPI you type. This page solves for the DPI. One slug covers both the photo and the printing names.
Assumptions
- The print size is the finished image, not the paper.
- Pixels are not resampled.
- The limiting side is the one that sets sharpness.
Worked example
A 2400 by 3000 pixel file printed at 8 by 10 inches is 300 DPI.
Input definitions
- Limiting DPI
- The less dense of the two sides.
- Print size
- The width and height of the image on paper, in inches.
Limitations
This is a planning figure from the numbers you type. It is not a measurement of a network, a camera, a printer, or a power supply.
Questions
Why the smaller side?
If one side is coarser, that side sets the detail the print can hold.
Where do I start from a DPI?
On the print-size page, which turns pixels and a DPI into inches.